This summer I’ve been taking a Biology class at my community college, and I learned a Thing™.
Organisms as we typically think of them are classified into two domains: Bacteria and Eukarya. There’s also a third domain–Archaea–but you probably wouldn’t know any of those guys unless you have microscopic vision and hang out in extreme environments like deep-ocean vents, or spend a lot of time looking into your own navel.
Either scenario presents its own special danger.
Domain Bacteria contains microorganisms such as germs and cooties. They are prokaryotes, with cells that lack the nuclei and organelles found in more complex organisms.
Plants and animals fall within Domain Eukarya. As eurkaryotes, their cells contain both membrane-bound nuclei and organelles that perform specialized functions, such as energy production and protein replication.
Scientists have theorized that prokaryotes appeared first, followed by eukaryotes. In order to explain how such a thing could be, they developed the Endosymbiotic Theory.
This theory proposes that the first eukaryotic cell was originally a prokaryotic organism that happened to have a nucleus, which then consumed another prokaryote in a scene that probably looked something like this:
“I happen to have a nucleus and I sure am hungry. Oh, hello, fellow prokaryote…nice to eat you…I mean MEET you. Aw, screw it…GET IN MAH BELLEH!”
*NOM NOM NOM*
But then something strange happened that altered the course of the world…
“Good gravy! Something strange is happening that will alter the course of the world…what is wrong with mah belleh?”
*RUMBLE RUMBLE RUMBLE*
Rather than being digested like a recalitrant cheeseburger, the engulfed prokaryote incorporated itself into the structure of its devourer, and together they became the first eukaryotic organism.
“Whew, I feel better now. And I’ll be darned if I don’t suddenly have improved powers of energy production…”
Scientists have offered evidence to support the Endosymbiotic Theory, pointing to two organelles in particular–the chloroplast and the mitochondrion, which function as energy-production structures in plant cells:
1. The DNA of a eukaryotic cell is stored in the nucleus, but chloroplasts and mitochondria contain their own DNA and can even manufacture proteins, such as the microscopic equivalent of beef jerky.
2. Chloroplasts and mitochondria are roughly the same size as bacteria, which, of course, they would be if they were once organisms that were minding their own business until something came along and ate them.
3. Chloroplasts and mitochondria have double membranes–an inner one similar to that found in prokaryotic cells, as well as an outer one like those of eukaryotic cells. I’ve seen this kind of thing before in bags of candy. When globs of chocolate devour almonds, well…the almonds are still inside.
4. Like prokaryotes, chloroplasts and mitochondria reproduce through binary fission, a process I shall now demonstrate through the medium of interpretive dance:
“Hi, I’m a chloroplast. I’m green and pretty awesome. You know what would be more awesome? Two of me!”
I thought this whole idea was pretty interesting until I realized something. Animals don’t have chloroplasts–in much the same way that Trix is for kids and not for rabbits–but they do have mitochondria.
Humans have mitochondria too.
If endosymbiosis happened before, what if it happens again? I just ate a sandwich. Rather than dissolving into questionable nutrients like it’s supposed to, is it even now incorporating itself into my structure as some strange new internal organ made of whole wheat and turkey?
This is the kind of thing that keeps me awake at night…
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What cool Thing™ have you learned that sparked your imagination? And what did you have for lunch today? 😉